Overproduction of ?-amyloid (A?) is widely believed to trigger a cascade of neurodegeneration leading to Alzheimer's disease (AD). A? is proteolytically derived from ?-amyloid precursor protein (APR) through sequential cleavages by ?-secretase (BACE1) and ?-secretase complex (consisting of four components: presenilin, nicastrin, APH-1 and PEN-2). Much research effort has gone into studying regulation of secretase activity at the post-translation level, transcriptional regulation of gene expression of secretase components, the first step of any protein's biogenesis, has been much less explored. Recently we and others have characterized the basic promoter sequence for BACE1, presenilins, PEN-2 and APH-1, and several identified transcriptional factors. However, additional transcriptional factors and related regulatory mechanisms/pathways still remain to be identified. Questions such as how transcriptional events may differentially affect the secretase activity in different cell/tissue types, and the importance of the transcriptional regulation of the secretase components in AD pathogenesis are highly important and remain to be addressed. Based on the available information and our preliminary results, we propose to study the following aims:
Specific Aim 1 : to further characterize the transcriptional regulation of BACE1 by HIF/hypoxia and A?, to determine the cell type specificity of promoter utilization for BACE1, and to correlate the importance of the transcriptional regulation of BACE1 gene in AD pathogenesis. We will (1) determine whether transcription of BACE1 is regulated by HIF-1 and whether HIF-1 deficiency affects BACE1 expression in vivo;(2) determine whether expression of BACE1 transcription factors (i.e. SP1 and HIF-1) and their activity are altered in AD brains;(3) determine transcriptional regulation of BACE1 in neuronal and non-neuronal cells;and (4) study a potential reciprocal regulation between A? and BACE1, i.e. to determine whether A? treatment regulates transcription of BACE1.
Specific Aim 2 : to define the promoter and transcriptional regulation of nicastrin, to determine the cell type specificity of promoter utilization for various ?-secretase component genes and their transcriptional regulation by A?, and to correlate the importance of the transcriptional regulation of these genes in AD pathogenesis and in controlling the ?-secretase substrate specificity. We will (1) characterize promoter and transcriptional regulation of nicastrin gene;(2) determine whether the levels of transcription factors regulating expression of ?-secretase components are altered in AD brains;(3) define the cell type specific transcriptional regulation of genes encoding the four ?-secretase components;(4) determine whether A? treatment promotes the expression of ?-secretase components;and (5) determine the effects of transcriptional regulation on the ?-secretase activity to different substrates. Studying transcriptional regulation of these secretase components should be instrumental for developing effective therapies for AD.
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